hi prof hwang,
i doubt anyone else is going to give any sample codes to refer to on this :)
chance to help me out here?  how to make magnet1 and magnet2 in a single applet with different rotation with vector sum of the magnetic field vectors?

http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=1602msg6056;topicseen#msg6056

the problem happens when cta =! cta2.

thanks!